If you're not satisfied with the two major parties, why can't you vote for a third party?
Sweden has lots of parties. New ones pop up now and then.
List of political parties in Sweden - Wikipedia, the free encyclopedia
Sometimes they die after a few years. There was a party that started up, got into parliament and stirred things up for a while and then disappeared. They had a lasting effect on the bigger parties even if they didn't hang around for long.
Others keep on fighting with the few voters they have, we have a party that's a bit hostile towards immigrants. They generally have a bad reputation and most people think it should be shut down, but we live in a democracy so even nazis have the right to vote and form parties. They deny being racist or having nazi sympathies but lots of people see them as both. This party has seats in a few small communities and discontent citizens sometimes vote for them just to scare the bigger parties when parliament does bad stuff.
In some cases a new party comes along that has a very good ideology. Our socialist party started off by focusing on worker issues and is now our biggest party. The Green party started with their environmental issues and now play a big part in our parliament. I don't know which parties are the original ones that took power away from the king, they're not really important anymore.
Lately we have a new and fresh party called the Pirate Party. May sound like a joke name, and in a way it is, but the party is very serious and has certainly become the party to vote for if you don't like that our parliament is dismantling our human rights.
Last but not least (just kidding, it is the least actually), people can vote for whatever the hell they want. A few voters choose to write the name of some famous person, a fictional character or various jokes. They may also draw some doodles and vote for that, but not many people choose to do so.